igneous
Basalt (River Stone)
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black with light plagioclase flecks; Luster: Dull/Matte (external) to vitreous (internal); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black with light plagioclase flecks
- Luster
- Dull/Matte (external) to vitreous (internal)
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black with light plagioclase flecks; Luster: Dull/Matte (external) to vitreous (internal); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
Formation & geological history
Extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. This specific specimen has been rounded by mechanical erosion in a fluvial (river) environment.
Uses & applications
Commonly used in landscaping (river rock), construction aggregate, road base, and therapeutic massage (hot stones) due to heat retention properties.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the entirety of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its heavy weight (dense), dark color, and fine-grained texture. It often shows small white specks of plagioclase feldspar. Common on beaches and in riverbeds worldwide.
